This invention relates generally to an aircraft wing adapted for subsonic cruise conditions very near Mach One, and more particularly to a laminar wing adapted for such transonic cruise conditions.
Modern subsonic aircraft designed for efficient cruise at high subsonic speed have moderate to highly swept wings (30° to 45°) with moderately high aspect ratio (5 to 8), supercritical airfoils and t/c (thickness/chord) ratios as thin as possible, typically about 10 to 12% for structural weight considerations.
The latest fighters on the other hand, have much thinner airfoils, typically about 3 to 5% t/c as a compromise in order to also have supersonic dash capability, with similar leading edge sweep, but low aspect ratio (3 to 5), such that the trailing edge is nearly unswept.
Prior patent art of one of the present inventors (Tracy) describes a wing for efficient supersonic cruise which has a relatively unswept (≦30°) and sharp “supersonic” leading edge, and t/c less than about 2% as a spanwise average, except in the immediate vicinity of the area-ruled fuselage. See U.S. Patents listed below. This wing achieves lower supersonic drag compared to the typical swept or delta wing traditionally selected for efficient supersonic cruise by achieving extensive areas of laminar boundary layer coverage, which provide nearly an order of magnitude reduction in associated skin friction. The extremely low thickness is required to limit wave drag due to thickness to acceptable levels, and necessitates a low aspect ratio (2.5 to 3) for structural weight reasons. The sharp-edged airfoil is biconvex or a minor modification thereof for low wave drag due to thickness and favorable pressure gradient. The low sweep is necessary to limit boundary layer crossflow to “subcritical levels” to prevent premature transition from laminar to turbulent boundary layer flow caused by so-called crossflow instability.